1. Field of the Invention
The present invention relates to a method of producing a hollow bodied component, and, more particularly, to a nondrawable component pf cellular or expanded synthetic material, such as polystyrene, by injection moulding.
2. Description of the Prior Art
The numerous advantages of cellular synthetic material such as expanded polystyrene have resulted in a rapid and important development in the use of cellular synthetic material in very different areas, such as the thermal insulation of buildings, packing material in packaging and more recently the use of such material to form disposable patterns for casting components in production lines.
For nearly twenty years in the casting industry, disposable patterns have been produced in expanded polystyrene. This method is still used for producing heavy components such as frames for machinery. In order to make such components, blocks or plates of desired dimensions are used together in order to form the shape of the desired pattern. The pattern is placed in the casting sand and the sand is packed down. The metal which can be aluminium is poured in the mold. The hot liquid metal melts in the pattern comprised of expanded polystyrene and the metal fills the space occupied by the pattern.
In recent years a technique has been developed for producing large quantities of medium-sized and small cast components because of the development of weaker granularity, lower density and brass formation characteristics of synthetic materials have evolved a great deal during the course of the last few years. The new techniques allow the injection molding of components with thinner walls having a better surface quality which has led to further development of producing castings using disposable patterns made of expanded polystyrene.
This technique is of particular interest in the automobile industry for the manufacture of components with interior cavities, such as, for example, intake or exhaust manifolds. The new techniques are very interesting because of the considerable reduction in the manufacturing costs of the cast components. There are still difficulties when producing certain castings because in the above case of intake and exhaust manifolds, the only method of producing disposable casting patterns consists in producing components having complex shape with a hollow and non-drawable, in two sections of expanded polystyrene, then drying the sections, and placing each section of the component on a template. Thus the sections are then joined together by adhesive such as "Hot Melt Glue".
Although this method of manufacturing is more interesting than the traditional method of moulding, it nevertheless has a number of disadvantages. It is necessary to carry out cold joining of the sections after moulding, which results in material increase in the cost of manufacturing the component. Furthermore, the component does not provide an interior and exterior surface having a required good quality because of the joint, and the seams between the adjoining sections.